1. Field of the Invention
The present invention relates to a method of manufacturing a color cathode ray tube apparatus and, more particularly, to a method of manufacturing a color cathode ray tube apparatus having a magnetic member arranged at least either inside or outside a neck in which electron guns are housed.
2. Description of the Related Art
A conventional color cathode ray tube apparatus includes a tube having a panel 2, a funnel 4 continuous with the panel 2, and a cylindrical neck 6 connected to the funnel 4, as shown in FIG. 1. A shadow mask 12 is arranged inside the panel 2, and a phosphor screen 5 consisting of light-emitting layers for emitting three colors, i.e., red, green, and blue, is formed on the inner surface of the panel to oppose the shadow mask 12. Electron guns 7 for emitting three electron beams B.sub.R, B.sub.G, and B.sub.B are housed in the neck 6. A deflection unit 14 is arranged outside a boundary portion between the funnel 4 and the neck 6 to horizontally and vertically deflect the three electron beams B.sub.R, B.sub.G, and B.sub.B emitted from the electron guns 7. In addition, a magnet 9 for adjusting static convergence and color purity is arranged outside the neck 6.
The above-mentioned magnet 9 is constituted by three pairs of annular permanent magnets respectively having two, four, and six magnetic poles. The annular permanent magnets are rotated about the tube axis (Z axis) to change the positions of magnetic poles. With this operation, static convergence and color purity are adjusted.
The above-mentioned adjustment of static convergence and color purity is manually performed. Since this adjustment is complicated, even a skilled operator requires much time to perform it.
FIG. 2 shows another conventional apparatus designed to solve the problem of adjustment of static convergence and color purity which is performed by the magnet 9. In this apparatus, one or more magnetizable annular magnetic members 11 are arranged around electron guns 7 housed in a neck 6 in place of the magnet 9. In this case, the magnetic member 11 is polarized and magnetized to obtain two, four, six, and twelve magnetic poles during test and adjustment operations in the final assembly process of a color cathode ray tube apparatus. With this arrangement, the same effect as obtained by the magnet 9 can be obtained.
Methods similar to the above-described polarization/magnetization method are disclosed in Published Unexamined Japanese Patent Application Nos. 52-117517 and 54-18235 and Published Examined Japanese Patent Application No. 63-7420. These three conventional methods will be described below.
First, in the method disclosed in Published Unexamined Japanese Patent Application No. 52-117517, static convergence and color purity are adjusted in advance by an adjusting unit. Magnetizing currents are supplied from this adjusting unit on the basis of adjustment information, and DC magnetic fields are generated by using magnetizing coils, thus magnetizing a magnetic member.
In this method, when the magnetic member is to be magnetized to have a plurality of magnetic poles, its magnetization state cannot be accurately controlled for the following reasons. For example, a combination of two, four, and six magnetic poles are to be obtained, the state of each magnetic pole obtained by magnetization is easily changed. In addition, owing to the magnetization characteristics of the magnetic member, a linear relationship is not established between the magnetizing force of a desired magnetic pole and a magnetic field at an accurate position of magnetization. In this method, therefore, it is very difficult to magnetize the magnetic member to obtain a combination of two, four, and six magnetic poles. Furthermore, when magnetization is performed to obtain the respective poles, the magnetic characteristics of portions, of the magnetic member, other than the magnetic poles are changed. For this reason, two, four, and six magnetic poles cannot be sequentially obtained. With regard to a magnetic member in the neck, since the distance between the magnetic member and magnetizing magnetic poles is large, a magnetic flux diverges, and magnetization cannot be accurately controlled, as described above.
Second, in the method disclosed in Published Unexamined Japanese Patent Application No. 54-18235, magnetization is performed by causing magnetization saturation of a magnetic member on two sides of a hysteresis curve using an attenuation alternating field. When the magnetic member is magnetized by an attenuation alternating field, hard magnetization is left in the magnetic member after the alternating field is attenuated. This hard magnetization neutralizes a magnetic field externally applied to the magnetic member so as to reverse the direction of the external magnetic field. As a result, a desired magnetic pole can be formed after the external magnetic field is removed.
In this method, in order to leave a magnetized portion, in the magnetic member, which has a linear relationship with an external magnetic field, an attenuation alternating field which is uniformly changed in strength must be applied to the entire magnetic member. In addition, the initial maximum value of an attenuation alternating field must be set to be larger than the coercive force of the magnetic member. If, therefore, a magnetic member is composed of a magnetic material having a large coercive force, the magnetic member cannot be completely magnetized. That is, a magnetic member having a large coercive force cannot be used in this method.
Third, in the method disclosed in Published Examined Japanese Patent Application No. 63-7420, a magnetic member is heated to a temperature equal to or higher than a temperature corresponding to a magnetic transformation point or to a temperature high enough to eliminate spontaneous magnetization. Thereafter, magnetic fields generated by a multipolar field generator are applied to the magnetic member to form magnetic poles at predetermined positions. The multipolar field generator has a plurality of magnetic pole forming members capable of selectively forming magnetic poles in predetermined directions.
According to this method, since hard magnetization can be left in the magnetic member, magnetic poles having desired strengths required to adjust the static convergence and color purity of a color picture tube can be formed.
Even if poles having desired strengths are formed by this method, since the multipolar field generator having the magnetic pole forming members is arranged during the formation of the magnetic poles, errors may occur in static convergence and color purity when a color picture tube is incorporated in a receiver.
As described, in the above-described methods, a magnetizable annular magnetic member is arranged around an electron gun assembly, and the magnetic member is polarized/magnetized to obtain two, four, six, and twelve poles, thereby adjusting static convergence and color purity. The following three methods are available as methods of polarizing/magnetizing a magnetic member:
(1) A method of generating DC magnetic fields by using magnetizing currents and magnetizing coils on the basis of information from an adjusting unit.
(2) A method using an attenuation alternating field to cause magnetization saturation of a magnetic member on two sides of a hysteresis curve.
(3) A method of heating a magnetic member to a temperature equal to or higher than a temperature corresponding to a magnetic transformation point or to a temperature high enough to eliminate spontaneous magnetization, and subsequently applying magnetic fields to the magnetic member to form magnetic poles at predetermined positions.
The method (3) of heating a magnetic member to a temperature equal to or higher than a temperature corresponding to a magnetic transformation point or to a temperature high enough to eliminate spontaneous magnetization, and applying magnetic fields to the magnetic member is effective in forming desired magnetic poles as well as the method (2). However, when a color picture tube is incorporated in a receiver, errors occur in static convergence and color purity. Such errors do not occur in the step of forming magnetic poles in a magnetic member by means of the multipolar field generator but occur when the generator is detached after desired magnetic poles are formed. It is found from an examination on the cause of these errors that the magnetic pole forming members of the multipolar field generator which are composed of a ferromagnetic material change the distribution of geomagnetism. For this reason, even if static convergence and color purity are accurately adjusted by using the multipolar field generator, once it is detached, the distribution of geomagnetism with respect to the color cathode ray tube apparatus is changed to cause errors.
A magnetic shield consisting of a magnetic material is arranged inside or outside a color cathode ray tube apparatus to minimize the influences of geomagnetism. Even with the magnetic shield, however, the influence of geomagnetism cannot be completely eliminated.
Under the circumstances, color cathode ray tube apparatuses are classified into types used in, e.g., the Northern hemisphere, in the Southern hemisphere, and in the equatorial area in accordance with the distribution state of geomagnetism. With this classification, color cathode ray tube apparatuses are adjusted to obtain good images in the respective areas.
Generally, a large number of nonmagnetic members are used for manufacturing equipment of a color cathode ray tube apparatus, especially test devices for such equipment. If a magnetic material is used, it is used in a manner not to disturb geomagnetism. In addition, a uniform magnetic field is applied to the entire color cathode ray tube apparatus, as needed, to prevent unexpected influences. However, when a magnetic member is arranged on a color cathode ray tube, and magnetic poles are formed in the magnetic member by generating magnetic fields from the outside of the color cathode ray tube apparatus, the magnetic pole forming members of the multipolar field generator must be arranged close to the magnetic member. In addition, in order to leave hard magnetization in the magnetic member, each magnetic pole forming member needs to have a core consisting of a ferromagnetic material capable of generating a magnetic field. Therefore, it is difficult to remove all magnetic materials from positions near the color cathode ray tube apparatus. That is, the geomagnetism cannot be completely free from the influences of the magnetic pole forming members.
A magnet for adjusting static convergence and color purity is arranged near a deflection yoke. When magnetic poles are formed in a magnetic member, the multipolar field generator is placed near the deflection yoke. For this reason, a magnetic field generated by the deflection yoke influences the electron gun assembly. More specifically, when the multipolar field generator is placed near the electron gun assembly, the external field distribution of the deflection yoke is changed. This is because the field is changed by a magnetizing yoke, of the multipolar field generator, consisting of a ferromagnetic material. Therefore, if the multipolar field generator is arranged at the neck, static convergence and color purity are changed. Alternatively, an induction current is generated in coils constituting the multipolar field generator due to a high-frequency field generated by the deflection yoke, thus generating a magnetic field. This magnetic field also causes a change in static convergence and color purity.
The change in static convergence and color purity which is based on the above-mentioned reason is small. For example, a static convergence change amount of a 25" 110.degree. deflection tube is about 0.1 mm. Such a small change amount normally falls within the error range of static convergence measurement. Therefore, no practical problems are posed except for cases wherein especially static convergence is of prime importance, or the rating margins are very small. However, such a change amount cannot be allowed in a display tube of the present invention, in which almost no variation in static convergence is allowed, and even a change amount of 0.1 mm or less poses a problem.